The weight compensation for the easy operability of a microscope or the mobility of the same in space and for the compensation in this regard of changes in weight at the microscope as a result of adding or removing additional devices to or from the microscope is carried out, in the case of a known stand “MS 1” from the applicant, via a compression spring, which supports a parallelogram carrier diagonally. In the case of the MS 1 design, this parallelogram carrier serves as a pivotable horizontal carrier for the microscope. The particular parallelogram construction has been disclosed by the applicant in the European Patent Application EP 433426 A1 (WO 91/472). The design of the MS 1 is illustrated symbolically in the international Patent Application WO 99/1693 (1999).
For the purpose of improved tilting behavior of the stand, the MS 1 provides a switch box as a balance weight, the box containing both the electrical power supply for the microscope and its lighting device, its control systems and the like and, if appropriate, an additional weight. The switch box is mounted rigidly on the vertical upright column of the stand and there performs only balancing around the vertical axis of the vertical upright column with regard to improving the tilting moment of the stand.
DE 19742050 A1 (1999) makes reference to an article “Gewichtsausgleich an feinmechanischen Geräten” [Balancing on precision mechanical devices] by H. Hilpert in Issue February 1965 of the Journal Feingerätetechnik [Precision Engineering], Volume 14.
In this article, from the year 1965, various weight-compensating measures in precision engineering are discussed, being achieved primarily not by counterweights but by means of spring-compensating measures (such as, by way of comparison, also in the case of the parallel support construction of the MS 1).
DD 221571 A1 (1985) shows a stand design having a lever arm which is weight-compensated by a spring that is connected to the lever arm via a cable pull. The surgical microscope is located at the distal end of the lever arm. The basic adjustment of this surgical microscope is performed via a threaded spindle, with which the end of the spring fixed to the frame is drawn further away from the lever arm or guided closer to it. Changes in weight at the microscope are compensated for by the fact that the pivoting point of the cable pull relative to the lever arm is adjusted via a spindle.
In order to achieve a uniform countermoment in all the possible angular positions of the stand, it is necessary for the aforementioned point of action of the cable pull to be located on a connecting line between the axis of rotation of the lever arm and the mass center of gravity of the microscope. This is achieved by operating an adjusting device in the form of a worm, which rotates a disc connected to the lever arm about the axis of rotation of the lever arm.
In this design, a range of adjustment measures are therefore necessary in order to achieve the desired effect. Apart from this, the construction of this known design necessitates a high overall center of gravity of the stand, since all the balancing devices are arranged above the microscope.
DE 3739080 A1 (1989) likewise specifies a spring device for balancing for stands in which cable pulls in combination with springs are intended to lead to balancing. However, this concerns the provision of force support for an adjusting movement which is exerted by an operator on a handle. However, it does not concern holding a load in a “floating state”, as is desired in the case of surgical microscopes.
By contrast, U.S. Pat. No. 5,397,323 (1992) presents a surgical robot having parallelogram carriers, in which, inter alia, the weight of the instrument is held in a weight-compensated fashion via a cable pull with the aid of a counterweight. In this case, the cable pull is of closed design, that is to say one cable in each case is guided from the instrument up to the counterweight over an upper and lower deflecting roller (FIG. 3 of US -323).
Such a design presupposes that the counterweight is fitted in the immediate vicinity of the instrument. It could therefore be applied only poorly for use on a surgical microscope.
DE 19742050 A1 (1999) discloses a stand design having a pivotable parallelogram carrier which is weight-compensated via a cable pull and a balancing spring such that the balancing weights are additionally present and which act in accordance with the balance principle mentioned above can be designed to be particularly small. In the case of this design, the cable pull is guided in a special way in order to minimize the balancing error caused by the finite deflecting radius over a wide pivoting range of the pivoting arm. The balancing error is, however, not eliminated by this measure, and so in specific pivoting positions, adjustment of the balancing weights is still required in order to achieve the desired balancing.
U.S. Pat. No. 6,070,839 (2000) discloses a further design having a pivoting arm and a cable pull-spring construction which permits pure balancing—in the sense of the above-mentioned diagonal parallel carrier arm compensation in the MS 1—but without also contributing balancing moments to an improvement in the tilt safety. In the case of changes in weight, the pivoting point of the cable pull is displaced over a spindle, in a way comparable to the design in the aforementioned DD 221571.
U.S. 5,253,832 (1999) describes a stand having a centrally arranged tension spring for the balancing. This design offers no simple adjustability for changed loads. The tension spring itself has a low inherent weight, so that although it is used for balancing, it is not used for the balance about the vertical mid-axis (tilt safety).
Furthermore, EP 700665 A1 (1995) specifies a stand design which substantially ensures balancing via levers and angled lever arms. In FIGS. 13 and 14 of this published Patent Application, a movement transmission mechanism 157 is presented, which transmits movements of the microscope body about movement axes to a pivoting arm. As a result of this very complicated design with many parts, although a certain amount of balancing is provided, a large number of levers and angled levers is required, since the balancing is ultimately mounted on such levers.
In the MS 1 of the applicant, and in various designs of other known stands, and in the stands specified above, the main support, which accommodates the load directly, is often not fixed directly to the vertical upright column of the stand, but to an additional horizontal arm projecting from this column. Tilt safety is primarily achieved in these designs by an appropriate construction of the stand foot, which must be appropriately large and heavy. The weight compensation, as already specified further above, is effected by a spring diagonally in the parallelogram carrier or by other measures specified above.
An improvement in the tilt safety and a certain compensation for tilt prevention may certainly—as specified above—be made possible by the special arrangement of a switch box or the like.